Phase shifting by novelty-induced running: activity dose-response curves at different circadian times.
This study compared phase shifting after novelty-induced running at different circadian times (CTs). In Experiment 1, hamsters were confined to novel wheels for 3 h, starting at CTs 2, 4, 6, 8, 10 or 22. The largest shifts were found at CTs 2, 4 and 6. At each CT there was a relationship between the number of revolutions during the pulse and the size of phase shift. Maximum shifts were usually observed at each CT when animals ran 5000-9000 revolutions during the pulse. In Experiment 2, hamsters were confined to novel wheels for 1 h, also starting at CTs 2, 4, 6, 8, 10 or 22. Unlike with 3-h pulses, the largest shifts with 1-h pulses occurred at CT 8. In Experiment 3, hamsters were shut into a small nest box after a 1-h pulse at CT 8; phase shifting was unaffected, showing that movement about the home cage after a 1-h pulse had ended was not required for shifting. At CTs 2, 4 and 22, 3-h pulses produced shifts but 1-h pulses did not. Possibly, there are two different mechanisms of nonphotic phase shifting that can be activated by being placed in a novel wheel, but the results can also be explained in terms of a single mechanism.
Bobrzynska
K J
KJ
Department of Zoology, University of Toronto, Ontario, Canada.
Mrosovsky
N
N
D000818:Animals; D002940:Circadian Rhythm / Q000502:physiology*; D006224:Cricetinae; D004305:Dose-Response Relationship, Drug; D004777:Environment; D008297:Male; D008647:Mesocricetus; D009043:Motor Activity / Q000502:physiology*